Rechargeable lithium batteries are light and are in commercial demand by the electronic industry as a high density energy source. Most rechargeable lithium batteries have a negative electrode or anode containing elemental lithium, either as lithium metal or lithium alloy, or more often intercalated in some form of carbon or in a compound capable of intercalating lithium ions. The rechargeable lithium battery also has a positive electrode or cathode containing a substance, usually a chalcogenide, capable of incorporating lithium in its structure, as the positive active component, a non-aqueous electrolyte which is conductive of lithium ions, and a pair of current collectors in contact with the anode and the cathode, respectively. The rechargeable lithium battery may also include separators to separate the electrodes from one another electrically. Rechargeable lithium batteries are usually sensitive to atmospheric oxidation and humidity, in other words, to maintain their electrical efficiency lithium batteries have to be protected from atmospheric oxygen, moisture and other corrosive reagents which may be detrimental to lithium ions.
There are known methods of providing protection for lithium batteries from oxidation, such as for example, encasing the battery in a metal container, or inserting the battery between rigid metal plate current collectors or in some instance between metallic foil current collectors, and placing a tight insulator frame around the periphery of the battery, thereby sealing and protecting the lithium battery from atmospheric corrosion.
Electrochemical cells sealed in flexible polymer containers are described in U.S. Pat. No. 4,092,464 issued to A. N. Dey et al. on May 30, 1978. The electrochemical cells of Dey et al. have lithium metal anodes and silver chromate cathodes, each electrode being sealed in an ionically conducting polymer pouch and having a terminal egressing from the pouch. The enclosed electrodes are placed in a polymer laminate bag which is subsequently filled with non-aqueous electrolyte. The terminals carry a coating of heat-sealable material which permits the formation of a seal between the polymer laminate bag and the terminals. Rechargeable lithium batteries are frequently made in the shape of thin film or thin plate batteries which are wrapped in a flexible multi-layered polymer laminate. There are several known laminated packaging materials composed of layers impervious to oxygen and/or moisture, which have been utilized in packaging and protecting lithium batteries from damage caused by oxidation, such as for example, those described in U.S. Pat. No. 5,326,652 issued to R. C. Lake on Jul. 5, 1994, and U.S. Pat. No. 5,591,540 issued to Louie et al. on Jun. 7, 1997. Thin plate rechargeable lithium batteries are usually equipped with two electrically conducting extensions which are used as terminals for connecting the battery in serving as a power source, as well as for charging the battery. None of the above mentioned patents give detailed teachings with respect to the manner of sealing the terminals to the packaging laminate of the battery. R. A. Austin et al. in U.S. Pat. No. 4,997,732 which issued on Mar. 5, 1991, teach a lithium battery constructed of cells made of lithium foil anode, vanadium oxide cathode and a polymer electrolyte between them, enclosed in a moisture impervious multi-layered material having a heat-sealable polymer inner layer. The multi-layered material of Austin et al. may include another thermoplastic polymer, a metallic foil as a moisture and oxygen barrier, and an outer polymer protective layer. It is apparent that the laminate layers are sealed to one another and to the metallic current collector terminals of the packaged cell in a single process step. Austin et al. make brief reference to the need for adhesion between the surface of the metallic terminal and the heat sealable inner layer but provide no detailed instruction on how this is achieved. It is known that the polymer laminates can be durably bonded together by applying heat and pressure, however, the bond between the metal surface of the tabs or terminals and the polymer may not be sufficiently air-tight, and oxygen and/or moisture may enter at the metal-polymer interface into the battery package unless strong adherence between the metal and the plastic or polymer laminate can be implemented.
Another defect that may arise in conventionally packaged rechargeable lithium batteries, wherein the metal foil located between the protective layers comes in contact with one or both the metallic terminals or tabs resulting in an electrical short within the battery. Such defect may be caused by the heat sealing process diminishing the thickness of the polymer layer, or the sharp edges of the metal terminal may cut through to the enclosed metallic foil or by similar events.